To convert any list into a complicated nest of dictionaries for ultra fast lookup.

ToMultiKeyDictionary.vb

<ExtensionAttribute()>
    Public Function ToMultiKeyDictionary(Of TSource, TSecKey)(ByVal source As IEnumerable(Of TSource), ByVal ParamArray func() As Func(Of TSource, TSecKey)) As IDictionary
 
        'EXAMPLE USAGE
        'dict = students.ToMultiKeyDictionary(
        '    {
        '         Function(x) x.Age, 
        '         Function(x) x.Location, 
        '         Function(x) x.Job, 
        '         Function(x) x.Name, 
        '         Function(x) x})

 
        Dim reverseCollection As New Dictionary(Of Integer, Type)
        Dim functionsCount As Integer = func.Count
        Dim dictTypeCollection As New List(Of IDictionary)
 
        Dim instanceOfCurrentDictionaryArgument As New Object
        Dim dictionaryArgQueue As Object = Nothing
        Dim dictionaryTypes As New List(Of Type)
 
 
 
        For i = 0 To functionsCount - 1
            reverseCollection.Add(i, source.Select(func(func.Count() - (i + 1))).FirstOrDefault().GetType())
        Next
 
 
        Dim typeOfGenericDictionary As Type
        Dim dictionaryTypeArgs() As Type
        Dim newConstructedType As Type
        Dim currentDictionaryInstance As IDictionary
 
        For i = 0 To reverseCollection.Count - 1
 
            If reverseCollection(i) IsNot GetType(String) Then
 
                instanceOfCurrentDictionaryArgument = Activator.CreateInstance(reverseCollection(i))
 
            Else
                instanceOfCurrentDictionaryArgument = String.Empty
 
            End If
 
 
 
            If instanceOfCurrentDictionaryArgument IsNot Nothing AndAlso dictionaryArgQueue IsNot Nothing Then
 
                typeOfGenericDictionary = GetType(Dictionary(Of ,))
                dictionaryTypeArgs = {instanceOfCurrentDictionaryArgument.GetType(), dictionaryArgQueue.GetType()}
                newConstructedType = typeOfGenericDictionary.MakeGenericType(dictionaryTypeArgs)
                currentDictionaryInstance = Activator.CreateInstance(newConstructedType)
                dictionaryTypes.Add(newConstructedType)
                dictionaryArgQueue = currentDictionaryInstance
 
 
            Else
                dictionaryArgQueue = instanceOfCurrentDictionaryArgument
            End If
 
 
        Next
 
 
        Dim dict As IDictionary = Activator.CreateInstance(dictionaryTypes.Last())
 
 
        'If dict IsNot Nothing Then
        Dim queueObj As Object
        For Each item In source
 
            Dim currentItem = item
 
 
 
            Dim newObject1 = Activator.CreateInstance(dict.GetType)
 
 
            Dim iterDict As IDictionary = dict
            
            Dim itemAddedFlag As Boolean = False
            Dim currentItemInCollection As IEnumerable(Of TSource)
 
            For i = 0 To func.Count - 1
 
 
                currentItemInCollection = source.Where(Function(x) x.Equals(currentItem))
 
 
                Dim currentKey As TSecKey = currentItemInCollection.Select(func(i)).FirstOrDefault()
 
 
                If iterDict.Contains(currentKey) AndAlso iterDict(currentKey) IsNot Nothing Then
                    iterDict = iterDict(currentKey)
                Else
 
                    queueObj = Nothing
 
 
                    For k = 0 To reverseCollection.Count - 1
 
                        If queueObj Is Nothing Then
 
                            queueObj = currentItemInCollection.Select(func(functionsCount - (k + 1))).FirstOrDefault()
 
                        Else
 
                            Dim curObject As Object = currentItemInCollection.Select(func(functionsCount - (k + 1))).FirstOrDefault()
                            Dim currentDictionaryFromReverse As IDictionary = Activator.CreateInstance(dictionaryTypes(k - 1))
 
                            If iterDict.GetType() = currentDictionaryFromReverse.GetType() Then
 
                                iterDict.Add(curObject, queueObj)
                                itemAddedFlag = True
                                Exit For
 
                            End If
 
 
                            currentDictionaryFromReverse.Add(curObject, queueObj)
                            queueObj = currentDictionaryFromReverse
 
                        End If
 
                    Next
 
                    If itemAddedFlag Then
                        Exit For
                    End If
 
 
                End If
 
            Next
 
        Next
 
        Return dict
    End Function